The structures of 5-diazouracil, 5-diazouridine and 5-diazo-2'-deoxyuridine have been the subject of several investigations. Originally, 5-diazouracil was prepared by decarboxylation of 5-diazoorotic acid(Behrend and Ernert, as reported in Ann. Chem., 258, 347 (1890). Several compounds were isolated in the Behrend and Ernert investigation, including an anhydride, a hydrate and an ethanol adduct of 5-diazouracil. These compounds were assigned, respectively, the following structures: ##STR2##
The assigned structures, however, have been reinvestigated. See Thurber and Townsend, A Reinvestigation of the Structure for 5-diazouracil, 5-diazouridine, 5-diazo-2'-deoxyuridine and Certain Related Derivatives by Proton Magnetic Resonance Spectroscopy, J. Hetero, Chem., 9, 629, (1972). This reinvestigation was conducted because the above-assigned structures failed to explain certain properties of 5-diazouracil and related compounds, and because 5-diazouracil and related compounds failed to react under conditions typical for diazo compounds.